So-called “inkjet printers” are widely used now to print characters, or images, etc. on sheets or the other article. The inkjet printer prints by spraying print paper with fine droplets of ink.
Recent applications of the inkjet printer technology are found in, among others, the forming of fine patterns on liquid crystal display color filters and conductor patterns on printed wiring boards. Conventionally, these patterns were formed by photolithography.
Active development programs are being implemented to apply the inkjet technology to, for example, fine dot forming devices which are able to form fine patterns with high accuracy by applying fine ink dots to a print target object (for example, a liquid crystal display color filter or a printed wiring board).
The fine dot forming device needs an inkjet head which ejects ink at a print target object in a stable manner and delivers ink dots to desired positions with high accuracy.
Incidentally, to apply fine ink dots to a print target object, the droplet of ink ejected from the inkjet head needs to be controlled so that it has as small a diameter as, for example, 10 μm or even less. However, as the shape of liquid is in a smaller size, a ratio between a cross-sectional area of the shape of the liquid over the inertial mass of the liquid becomes larger. The cross-sectional area accounts for air resistance of the liquid. In any ejection method that does not accelerate fluid while it is flying in the air, such a smaller size of the liquid therefore results in poor accuracy in the delivery of ink dots at desired positions.
Accordingly, to precisely deliver the fine ink dots as described above onto a print target object, an inkjet scheme based on electrostatic attraction is used in which an electrostatic force is applied to the fluid while it is flying in the air.
To spray fluid to the print target object using the inkjet head of the electrostatic attraction scheme like the one above, there is needed an electrolysis highly concentrated at the fluid's meniscus formed at a surface of a nozzle of the inkjet head.
To effectively develop a high concentration of electrolysis at the meniscus, the nozzles suitably have a tubular structure whose fluid outlet is protruded as much as possible. For the smaller size of the ink dots to be ejected at the print target object, the size of the openings of the nozzles is desirably as small as possible.
A fine pattern forming device, e.g., as illustrated in FIG. 18, has been proposed as an inkjet device for ejecting fine ink dots as described above (Patent Literature 1 (Japanese Patent Application Publication, Tokukai, No. 2003-311944, published on Nov. 6, 2003). Patent Literature 1 discloses a structure in which a through-hole as a flow path (i.e., ejection fluid flow path) for a fluid to be ejected is formed in a silicon substrate and the through-hole has at one end an opening as a fluid outlet. Note that FIG. 18 illustrates a conventional art and is a cross sectional view illustrating various parts of the fine pattern forming device.
More specifically, as illustrated in FIG. 18, the fine pattern forming device as illustrated in Patent Literature 1, includes a silicon substrate 102, a main electrode 106, a supporting member 108, a counter electrode 107, and a flow path 109. The main electrode 106 and the supporting member 108 are provided to a surface 102a of the silicon substrate 102. The counter electrode 107 is provided to face a reverse side of the silicon substrate 102 with a predetermined distance between the counter electrode 107 and the reverse side 102b. The flow path 109 is configured to supply an ejection fluid into a space formed between the silicon substrate 102 and the supporting member 108.
The silicone substrate 102 has a plurality of fine holes 103 that pass through the silicone substrate 102 from the surface 102a to the reverse surface 102b. Inside each of the fine holes 103, a silicon oxide layer 104 is formed. Each of the fine holes 103 has an opening 103b opened in the reverse surface 102b. The opening 103b is exposed from that surface of the inkjet head which faces toward a print target object. Nozzles 105, made of silicon oxide, are formed to protrude from the reverse surface 102b of the silicone substrate. The nozzles 105 are integrated with the silicon oxide layers 104, respectively.
Patent Literature 2 (Japanese Unexamined Patent Application Publication, Tokukai, No. 2002-96474, published on Apr. 2, 2002) discloses a method for producing fine nozzles for a fine pattern forming device in which, as illustrated in FIGS. 19(a) to 19(e), a plating film is formed on a side wall of a through hole of a substrate, and the plating film forms a flow path. One end of the flow path acts as a fluid outlet. Note that FIGS. 19(a) to 19(e) illustrate a conventional art and are views illustrating the method for producing the fine nozzles.
More specifically, the method for producing the fine nozzles is realized with the following steps.
Firstly, silicon oxide is formed on a whole surface of a silicon substrate 202 (FIG. 19(a)). After that, a metal thin film is formed on one side surface of the silicon substrate 202, and then patterned by photolithography and etching, thereby to form fine openings on the metal thin film (FIG. 19(b)).
Then, the silicon substrate 202 is deep-etched with the metal thin film used as a mask, thereby to etch part of the silicon substrate 202 where the fine openings are to be formed. Thereby, through fine holes are formed (FIG. 19(c)). Further, the metal thin film is removed and a silicon oxide layer is formed on an internal surface of each of the through fine holes (FIG. 19(d)). Subsequently, a reverse surface of the silicone substrate 202 is etched, so that only the silicon substrate 202 is partially etched away while the silicon oxide layers formed inside the through fine holes are remained to be exposed and protruded from the etched surface of the silicone substrate 202 (FIG. 19(e)).
Patent Literature 3 (Japanese Patent Application Publication, Tokukaihei, No. 9-193400, published on Jul. 29, 1997) discloses an inkjet printer. The inkjet printer includes a nozzle head 301 made of a resin. The nozzle head 301 has a nozzle hole 303, which passes through the nozzle head 301 from a surface to a reverse surface thereof. A Ni plating film 304 is formed on an internal wall of the nozzle hole 303 and partly protruded in a cone-like shape from a tip portion of the nozzle hole.
The inkjet printer includes the nozzle holes 303 in plurality (two channels of nozzle holes 303 are illustrated in FIG. 20). The Ni plating film 304 is formed with all channels. Moreover, all the channels are electrically short-circuited with each other.
In the inkjet printer described in Patent Literature 3, each channel is configured such that ejection liquid 307 is held in a liquid flow path constituted by the nozzle head 301 and the Ni plating film 304. An ejection signal applying means 306 is connected to the Ni plating films 304, while a counter electrode 305 is provided to face with the nozzle head 301. The ejection liquid 307 is ejected toward the counter electrode 305 by electrostatic attraction caused by voltage applied by the ejection signal applying means 306, the result of which the ejection liquid 307 attaches to a print medium 308.
Moreover, Patent Literature 3 describes, as illustrated in FIGS. 21(a) to 21(d), a method for producing the nozzle provided to the inkjet printer having the above structure.
In the method for producing the nozzle, a nozzle head 301 having nozzle holes 301a is prepared firstly, the nozzle holes 301a passing through a resin member of the nozzle head 301 from a surface to a reverse surface thereof as illustrated in FIG. 21(a).
Then, a molding hole layer 302, made of copper, is connected to the nozzle head, the molding hole layer 302 having molding holes 302a internally in a taper shape (FIG. 21(b)). After that, an Ni layer 304 is formed by plating. That Ni layer formed on that surface of the nozzle which is to face a medium is removed (FIG. 21(c)).
Then, only the molding hole layer 302 is etched away with an etchant, such as concentrated nitric acid or aqueous ammonia, which dissolves copper only (FIG. 21(d)). As a result of the removal of the molding hole layer 302, the Ni layer 304 formed on the internal wall of the molding hole layer 302 becomes an outlet 309 having a shape protruding from the resin member of the nozzle head.
Moreover, Patent Literature 4 (Japanese Unexamined Patent Application Publication, Tokukaihei, No. 9-156109, published on Jun. 17, 1997) discloses an inkjet printer of electrostatic attraction type, which includes a nozzle substrate having nozzles, and a counter electrode substrate having protrusion sections positioned in correspondence with the nozzles, wherein the nozzle substrate and the counter electrode substrate are protruded toward a sheet transport plane.